They gave her courage. The Pants mysteriously held the attributes of her three best friends, and luckily bravery was one of them. She would give the Pants what meager gifts she had, but courage was the thing she would take.
This quotation, from chapter 23, appears just before Lena confronts Kostos and tells him how she feels about him. Until this point, Lena has been quiet, contemplative, and withdrawn, preferring to watch the world from a distance rather than engage with it directly. She considers herself a fearful person, too scared of getting hurt or rejected to open herself up to other people. When she imagines her friends, she admires their ability to see the world differently than she does. In the Pants, she feels as though some of her friend’s qualities are rubbing off on her. Bridget, in particular, is someone Lena considers to be brave, and she feels this bravery seeping in to her through the Pants. The girls all rely on the Pants for courage in some way, and this is Lena’s moment to rely on the Pants as she usually relies on her friends.
The “meager gifts” Lena believes she’s offering the Pants—and, by extension, her friends—are not as meager as Lena thinks. Although Lena lacks Bridget’s extroversion, Tibby’s honesty and forthrightness, and Carmen’s demonstrative devotion, Lena offers introspection, reflection, an artistic worldview, and her own kind of bravery to the Pants. The other girls are not afraid to fall in love, even when it means getting hurt. Lena’s gift is her belief in the importance of love, which she likely understands more than any other girl because she has been so long without it and she understands how blessed people are who have it. Lena pursues love despite her terror, pushing herself out of her shyness to take a chance on happiness.